From: Michal Hocko <mhocko@xxxxxxxx>
Subject: elf: enforce MAP_FIXED on overlaying elf segments
Anshuman has reported that with "fs, elf: drop MAP_FIXED usage from
elf_map" applied, some ELF binaries in his environment fail to start with
[ 23.423642] 9148 (sed): Uhuuh, elf segment at 0000000010030000 requested but the memory is mapped already
[ 23.423706] requested [10030000, 10040000] mapped [10030000, 10040000] 100073 anon
The reason is that the above binary has overlapping elf segments:
LOAD 0x0000000000000000 0x0000000010000000 0x0000000010000000
0x0000000000013a8c 0x0000000000013a8c R E 10000
LOAD 0x000000000001fd40 0x000000001002fd40 0x000000001002fd40
0x00000000000002c0 0x00000000000005e8 RW 10000
LOAD 0x0000000000020328 0x0000000010030328 0x0000000010030328
0x0000000000000384 0x00000000000094a0 RW 10000
That binary has two RW LOAD segments, the first crosses a page border into
the second
0x1002fd40 (LOAD2-vaddr) + 0x5e8 (LOAD2-memlen) == 0x10030328 (LOAD3-vaddr)
Handle this situation by enforcing MAP_FIXED when we establish a temporary
brk VMA to handle overlapping segments. All other mappings will still use
MAP_FIXED_NOREPLACE.
Link: http://lkml.kernel.org/r/20180213100440.GM3443@xxxxxxxxxxxxxx
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Reported-by: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Khalid Aziz <khalid.aziz@xxxxxxxxxx>
Cc: Andrei Vagin <avagin@xxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Abdul Haleem <abdhalee@xxxxxxxxxxxxxxxxxx>
Cc: Joel Stanley <joel@xxxxxxxxx>
Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Cc: Mark Brown <broonie@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/binfmt_elf.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff -puN fs/binfmt_elf.c~elf-enforce-map_fixed-on-overlaying-elf-segments fs/binfmt_elf.c
--- a/fs/binfmt_elf.c~elf-enforce-map_fixed-on-overlaying-elf-segments
+++ a/fs/binfmt_elf.c
@@ -895,7 +895,7 @@ static int load_elf_binary(struct linux_
the correct location in memory. */
for(i = 0, elf_ppnt = elf_phdata;
i < loc->elf_ex.e_phnum; i++, elf_ppnt++) {
- int elf_prot = 0, elf_flags;
+ int elf_prot = 0, elf_flags, elf_fixed = MAP_FIXED_NOREPLACE;
unsigned long k, vaddr;
unsigned long total_size = 0;
@@ -927,6 +927,13 @@ static int load_elf_binary(struct linux_
*/
}
}
+
+ /*
+ * Some binaries have overlapping elf segments and then
+ * we have to forcefully map over an existing mapping
+ * e.g. over this newly established brk mapping.
+ */
+ elf_fixed = MAP_FIXED;
}
if (elf_ppnt->p_flags & PF_R)
@@ -944,7 +951,7 @@ static int load_elf_binary(struct linux_
* the ET_DYN load_addr calculations, proceed normally.
*/
if (loc->elf_ex.e_type == ET_EXEC || load_addr_set) {
- elf_flags |= MAP_FIXED_NOREPLACE;
+ elf_flags |= elf_fixed;
} else if (loc->elf_ex.e_type == ET_DYN) {
/*
* This logic is run once for the first LOAD Program
@@ -980,7 +987,7 @@ static int load_elf_binary(struct linux_
load_bias = ELF_ET_DYN_BASE;
if (current->flags & PF_RANDOMIZE)
load_bias += arch_mmap_rnd();
- elf_flags |= MAP_FIXED_NOREPLACE;
+ elf_flags |= elf_fixed;
} else
load_bias = 0;
_
--
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